Fluorescent lighting fixtures have been employed ubiquitously for the past several decades, in residences, offices, institutional, commercial, industrial, and a host of other environments, as energy-efficient alternatives to incandescent and other types of lighting fixtures that use less efficient light sources. Fluorescent light sources are significantly more efficient than incandescent light sources of an equivalent brightness, because more of the energy consumed by a fluorescent light source is converted to usable light and less is converted to heat (allowing fluorescent lamps to operate at cooler temperatures than incandescent and other light sources). In particular, an incandescent lamp may convert only approximately 10% of its power consumption into visible light, while a fluorescent lamp that produces as much useful visible light energy may require only one-third to one-quarter as much power. Furthermore, a fluorescent light source typically lasts between ten and twenty times longer than an equivalent incandescent light source. For at least the foregoing reasons, fluorescent lighting fixtures are popular choices for many lighting applications.
One conventional fluorescent lighting system is shown in FIG. 1. The illustrated fluorescent lighting system 100 is generally installed within an aircraft cabin to provide ambient illumination for aircraft passengers and crew. The system 100 includes at least one fluorescent lamp, at least one lamp control module (also known in the art as a power protection unit or PPU) and an inverter module. The inverter module 120 is connected to a DC power source in the aircraft to receive at its input a DC power (i.e., voltage and current). The inverter module 120 converts the DC power to an AC power, and outputs AC voltage and current to a lighting power bus 140. The inverter module 120 may also be connected to an input device such as a switch, cabin control unit, etc. in the aircraft (e.g., at a flight attendant station or in the cockpit) that may be operated/actuated by an aircraft crew member to output a dimming signal. Upon receiving the dimming signal (e.g., a momentary switch to ground signal), the inverter module 120 may vary the AC voltage and/or current at its output to dim or brighten the illumination intensity from the at least one fluorescent lamp.
As further shown in FIG. 1, the system 100 includes at least one PPU 160 and at least one fluorescent lamp 180 connected to each lamp control module 160. Although six PPUs 160 are shown with a total of twelve fluorescent lamps 180 connected thereto (the PPUs 160 and lamps 180 defining six areas or zones), the system could be configured otherwise. For example, fewer or additional lamps 180 and/or fewer or additional PPUs 160 may be provided relative to, for example, the configuration and/or number of inverter modules 120. As shown, the PPUs 160 are electrically connected to the bus 140 in a parallel configuration. Each PPU 160 receives AC power from the bus 140 and converts the AC input power to an appropriate AC output voltage and/or frequency to operate the one or more fluorescent lamps 180 connected thereto. The PPU 160 may include ballast-type circuitry for starting the fluorescent lamps 180, maintaining illumination thereof and protecting the system 100 and the lamps 180 in the event of a malfunction such as open or short circuits, broken output wires, improperly installed lamp connector assemblies, arcing, broken lamps or overheated lamp connectors/ends which occur as a lamp nears the conclusion of its life.
Although fluorescent lighting systems are more energy efficient than comparable incandescent lighting systems, fluorescent lighting systems that are installed in aircraft passenger cabins (e.g., the foregoing-described system 100 that is shown in FIG. 1) present aircraft operators with a number of challenges in operating and maintaining the systems. One challenge is that fluorescent systems employ glass lamps/bulbs that are subject to breakage, and therefore, are often difficult and/or time-consuming to replace safely. Furthermore, fluorescent bulbs use high voltage AC power (e.g., 1000Vp-p) and sometimes have a short service life (e.g., approximately 9000 hours) that requires airline operators to periodically inspect, maintain and replace bulbs that have failed or are near the end of their useful lives. Additionally, fluorescent bulbs emit ultra violet (UV) light that may cause plastic parts adjacent the bulb to become embrittled and/or break down over time. For example, UV light is known to affect exposed lamp connectors which may cause them to fail and result in a short circuit/arcing condition. Moreover, lamp control modules (i.e., ballast-like devices) of fluorescent systems often emit electromagnetic interference (EMI) which may interfere with other aircraft systems. Finally, fluorescent bulb systems are difficult to dim and illumination intensity is not typically customizable to a variety of levels. Conventional fluorescent systems are not continuously variable in their output illumination intensity and are instead generally constrained to discrete dimming levels (e.g., full brightness, off, and a brightness level intermediate off and full brightness). Additionally, when fluorescent bulbs/lamps are operated at dimmed illumination intensity (i.e., not full brightness), the useful life of the bulb/lamp is degraded/shortened.
In view of the foregoing-described challenges, it is desirable for airline operators to replace fluorescent-based lighting systems with light emitting diode (LED) based systems. However, existing replacement processes require aircraft operators to: 1) take an aircraft out of service for an extended period; access AC wiring and lighting system components (i.e., lamps and modules); and 2) replace existing AC wiring and lighting system components. At an average cost of $35M to have the aircraft on the ground to replace a fluorescent system with an LED based lighting system, it can be appreciated that existing replacement processes have significant drawbacks. In view of the foregoing, a new LED lighting system for an aircraft cabin that retrofits fluorescent lighting systems would be an important improvement in the art.